Sunday, April 03, 2005

The North Korean problem--and ours

China shares a 1200 kilometer border with North Korea in Jilin Province across the Yalu and Tumen rivers (Xinhua Net). Jilin is China's main agricultural province and largest poultry producer and exporter. Eastern Jilin's Yanbian Korean Autonomous Prefecture is home to over 800,000 Koreans who move back and forth between China and North Korea.

The 21 checkpoints at the Jilin border are also on high alert to stop the spread of bird flu from afflicted North Korea. All trade in live poultry or products that might transmit the disease are banned at the border markets and residents are prohibited from bringing live birds into or out of the country. Vehicles are being sterilized and poultry confiscated. Saturday over 120 kilo of chicken products were seized and destroyed on the spot. Jilin suffered H5N1 poultry infections in early 2004 when almost half of China's provinces were affected. That outbreak started in (South) Korea, so it is plausible it entered China in or near the Jilin border. The Chinese are clearly deeply concerned this will happen now. Beyond effects on poultry, public health officials must also be concerned that increased opportunities for reassortment (or possibly recombination) with human influenza viruses would result.

Now that Highly Pathogenic Avian Influenza (bird flu) has crossed the species barrier from bird to humans, the only remaining barrier to a full-fledged agent of pandemic disease is the ability to move easily from human to human. Given the size and scope of the Asian outbreak since late 2003, some people are asking if the apparent failure of efficient human transmission to develop is the result of some intrinsic biological barrier related to the H5N1 virus. For example, it could be that the required mutation or mutations involve some highly conserved region in one of the virus's genes. This is possible. But it seems unlikely, given what we know about the adaptability of this virus. It may be simply that we have been lucky so far or that the changed virus dead-ended in some remote village.

There is also another possibility. The transformation might already have taken place and produced (so far) relatively mild or inapparent infection. It should be remembered the first wave of 1918 flu (March 1918) was also relatively mild. The truly murderous onslaught came the following fall, in September. The increase in virulence might have been helped along by the extreme crowding in World War I military training barracks, troop ships and encampments. Under these conditions, just as in today's poultry "factory farms," a virus could kill rapidly and still be transmitted to another host. Whether this can happen without such permissive conditions is unknown. I hope we don't find out.